Shoulder strap assemblies used in bags, such as backpacks, typically use a two-part construction. An upper shoulder-engaging part of the strap assembly may include some cushioning for improved comfort and has one end fixed to the bag and the other end to a buckle. To adjust the length of the strap assembly a plain strap is fixed at a lower end of the bag and engages the buckle. In the conventional tension-locked buckle used in this application, the plain strap passes in a tight loop around a limb of the buckle, being firmly held in position when tensioned. This plain strap must be sufficiently flexible to cooperate with such a buckle and may be made from a woven or knitted synthetic fabric, leather or a like material.
For improved security of backpacks and other soft luggage, particularly against cutting, wire-reinforced fabrics have been used. In some constructions a wire mesh fabric may be laminated between the outer shell and the inner liner of the bag to provide improved security. However un-reinforced straps remain a point of weakness when the bag is being carried as they may readily be cut through by a hand-wielded blade, allowing a thief to quickly steal the complete backpack from the person carrying it. It should be noted that the term “backpack” is used herein in a broad sense to refer to any bag having a shoulder strap or waist strap by which it may be carried.
Parts of the strap assembly that are not readily visible when walking are vulnerable to being cut in this manner. Most vulnerable is the plain strap at the lower end, as it is also generally of minimum transverse dimensions and sits spaced apart from the carrier's body. Another vulnerable section is that extending generally behind the top of the carrier's shoulders to attach to the top of the backpack. While there is a need for improved security, particularly of these vulnerable portions, any new backpack shoulder strap should use conventional components as far as possible, to be cost-competitive.
It is an object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages or more generally to provide an improved backpack having an adjustable shoulder strap assembly able to deter cutting.